1. Field of the Invention
The present invention is directed generally to an arrangement for high-resolution spectroscopy including a wavelength selective diode array having different spectral sensitivities.
2. Description of the Related Art
Spectroscopic methods and analysis play a significant role in the fields of physics and chemistry. It is desirable in many applications to have a handy, compact spectrometer with which to perform spectroscopic analysis.
It is known to use photodiodes having "integrated" color filters as a spectrometer. See, for example, the publication of R. F. Wolffenbuttel, "Photodiodes in Silicon with an Intrinsic Color Filtering Capability", Proceedings of the International Conference on Solid State Sensors and Actuators--Transducers 87, Tokyo, pages 219-222, (1987) and F. Koike et al., "A New Type Amorphous Silicon Full Color Sensor", Proceedings of the International Conference on Solid State Sensors and Actuators--Transducers 87, Tokyo, pages 223-226 (1987). The disclosed devices utilize the fact that the penetration depth of optical radiation through silicon is wavelength dependent. The capture region for charge carriers and, thus, the entire wavelength-dependency of the photo current is controlled by the inhibit voltage applied to the diode. The disclosed photodiode is operated so that it has three color-sensitivity regions.
A publication of W. Albertshofer et al., "Flussigkeitsanalyse unter Verwendung einer Spektrometerdiode", Proceedings of Sensoren-Technologie und Anwendung, Bad Nauheim, FRG, 1986, NTG-Fachberichte 93, appendix page 30, discloses what is referred to as a spectrometer diode. The spectrometer diode is an arrangement of photodiodes which are side-by-side and which are sensitive in different wavelength regions. The diode is formed as a layered structure of a semiconductor material having continuously variable band spacing. The diode is irradiated from the side having the higher band spacing. Photons penetrate into the semiconductor material down to a depth in which they can be absorbed as a consequence of the band spacing. By beveling the backside of diode, it is possible to attach Schottky contacts at locations of different band spacing so that signals at corresponding different wavelengths can be received at the Schottky contacts.
The known diodes exhibit a resolution which is too low for many applications.